A method for preparing a millimeter-scale pure cubic phase KTN single crystal

Abstract

The application discloses a method for preparing millimeter-level pure cubic phase KTN single crystal, which comprises the following steps: placing KTN raw material at the bottom of a gold bushing tube, and then adding a mineralizer solution; sealing the gold bushing tube, and then placing the sealed gold bushing tube in a kettle body of an autoclave; adding water in the interlayer between the gold bushing tube and the kettle body, sealing the autoclave, and then placing the sealed autoclave in an electric resistance furnace for constant-temperature and constant-pressure treatment; uniformly reducing the temperature of the electric resistance furnace, and then rapidly reducing the temperature to room temperature after the temperature is reduced to 100 DEG C, so as to obtain millimeter-level cubic phase KTN single crystal. The millimeter-level pure cubic phase KTN single crystal prepared by the method can effectively improve the light transmission quality of the prepared product, and can also reduce the internal stress of the crystal and improve the light damage resistance of the crystal. The crystal prepared by the method has small thermal stress, few defects, high uniformity and high purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of crystal growth, in particular to a method for preparing millimeter-level cubic phase KTN single crystal by using a cooling hydrothermal method. BACKGROUND

[0002] Potassium tantalate niobate (KTN) is a famous ferroelectric material, which has a wide range of applications in electro-optics, nonlinear optics and other technical fields. When used as an electro-optic crystal, potassium tantalum niobate (KTN) can be used to make electro-optic devices such as electro-optic modulators, deflectors, Q-switches, and laser mode locking. These devices have a wide range of applications in frontier fields such as biomedical treatment, radar detection, laser display, and micro-nano processing.

[0003] The methods commonly used to prepare KTN crystals mainly include solid-phase sintering, melt pulling, high-temperature molten salt, and various process techniques developed on this basis, such as slow cooling, top seed pulling, and accelerated crucible rotation. These techniques have improved the composition uniformity and optical quality of KTN crystals to some extent. However, overall, KTN crystals prepared by these methods still have problems such as crystal cracking, and serious composition non-uniformity at different positions of large-size crystals, which severely affects the optical uniformity of devices. In addition, KTN crystals can exist in different crystal phases depending on the composition (Ta / Nb) and temperature. Generally, KTN crystals will undergo multiple phase transitions from high temperature to low temperature, such as cubic-tetragonal-orthorhombic-trigonal. Each phase transition produces a large number of phase domains, which not only affect the light transmission quality of the crystal, but also greatly increase the internal stress of the crystal, reducing the crystal's resistance to light damage.

[0004] Therefore, it is an urgent technical problem for those skilled in the art to provide a method for preparing millimeter-level pure cubic phase KTN single crystals. SUMMARY

[0005] In view of the above, the present application provides a method for preparing millimeter-level pure cubic phase KTN single crystals.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A method for preparing millimeter-level pure cubic phase KTN single crystals, comprising the following steps:

[0008] (1) Put KTN raw materials at the bottom of a gold bushing tube, and then add a mineralizing agent solution;

[0009] (2) Seal the gold bushing tube and place it in the body of an autoclave;

[0010] (3) Add water to the interlayer between the gold bushing tube and the autoclave body, seal the autoclave, and then place the sealed autoclave in an electric resistance furnace for constant temperature and pressure treatment;

[0011] (4) Set the resistance furnace to a cooling rate of 1-10℃ / h, and after the temperature of the resistance furnace is reduced to 100℃, rapidly reduce the temperature to room temperature to obtain the millimeter-level cubic phase KTN single crystal.

[0012] The millimeter-level cubic phase KTN single crystal is prepared by the hydrothermal method: under hydrothermal conditions, "dissolution" refers to the initial stage of the hydrothermal reaction, in which the agglomeration and connection between the precursor particles are destroyed, so that the particles themselves are dissolved in the hydrothermal medium in the form of ions or ion groups, and then nucleate, crystallize and form crystal grains; "crystallization" refers to the nucleation and growth of crystal grains in the system when the concentration of solute in the hydrothermal medium is higher than the supersaturation required for nucleation of the crystal grains. With the progress of the crystallization process, the concentration of the material for crystallization in the medium becomes lower than the solubility of the precursor, which allows the dissolution of the precursor to continue. This process is repeated until the reaction time is long enough, and the precursor is completely dissolved to form corresponding crystal grains.

[0013] Further, the KTN raw material in step (1) is a ground solid-phase sintered KTN polycrystal or a KTN crystal with poor uniformity prepared by the Czochralski method or a KTN leftover material.

[0014] Further, the ground solid-phase sintered KTN polycrystal is undersize material sieved by a 100-mesh sieve.

[0015] Further, the mineralizer solution in step (1) is a mixed solution of one or more of KOH, KNO3 and KF.

[0016] Further, the concentration of the mineralizer solution is 6-20 mol / L.

[0017] The beneficial effects of the above further scheme are that, since KTN has a high dissolution temperature (1200℃), the KTN crystal can be dissolved and crystallized at a much lower temperature than the melt method and flux method under the condition of the presence of the mineralizer solution. The mixed solution of one or more of KOH, KNO3 and KF as the mineralizer can promote the progress of the hydrothermal reaction. The mixed solution of one or more of KOH, KNO3 and KF is an alkaline mineralizer, and the KTN raw material has a high solubility in the alkaline mineralizer solution and can be quickly dissolved in a short time. The concentration of the mineralizer is a key factor affecting the size of the product.

[0018] Further, the total filling degree of the KTN raw material and the mineralizer solution in step (1) is 45-60% of the gold lining pipe.

[0019] Further, the filling degree of the water added to the interlayer of the gold lining pipe and the kettle body in step (3) is 45%.

[0020] The beneficial effect of the further scheme is that the filling degree in the gold bushing pipe is the inner filling degree, and the filling degree of the water added in the interlayer of the gold bushing pipe and the kettle body is the outer filling degree. The difference between the certain inner and outer filling degrees can guarantee the convection of the solution in the gold bushing pipe, so that the raw materials in the early stage can be fully dissolved in the gold bushing pipe, and the crystal grown in the later stage has small thermal stress, few defects, high uniformity and high purity.

[0021] Further, the temperature of the electric resistance furnace in step (3) is 500-600 DEG C, the pressure is 80-150 MPa, and the constant temperature treatment time is 5-10 days.

[0022] The beneficial effect of the further scheme is that the temperature and pressure of the crystal growth are important factors affecting the crystal component and size. Although the growth temperature of the KTN crystal can be much lower than that of the melt method and flux method, under the conditions that the high-pressure kettle equipment can withstand, the higher temperature of 500-600 DEG C and the pressure of 80-150 MPa can make the KTN raw materials fully dissolved without adding other surfactants or organic solvents (such as polyvinyl alcohol PVA). The constant temperature treatment time of 5-10 days can make the raw materials completely dissolved under the action of the mineralizer. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The structure diagram of the equipment used for the preparation method of the KTN single crystal of the application.

[0024] In the drawings, the components represented by each reference numeral are listed as follows:

[0025] 1 - furnace body; 2 - heater; 3 - high-pressure kettle; 4 - gold bushing pipe; 5 - mineralizer solution; 6 - raw material;

[0026] Figure 2 The XRD diagram of the KTN single crystal prepared in Example 1 of the application;

[0027] Figure 3 The size photo of the KTN single crystal prepared in Example 1 of the application;

[0028] Figure 4 The photo of the cubic phase KTN single crystal prepared in Example 3 of the application. DETAILED DESCRIPTION

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] (1) Take 10g of ground KTN polycrystalline material obtained by solid-state sintering and place it at the bottom of the gold bushing tube, then add mineralizing agent solution; the mineralizing agent is 20mol / L KOH; the total filling degree of KTN raw material and mineralizing agent solution is 50% of the gold bushing tube.

[0032] (2) After sealing the gold bushing, place it in the body of the autoclave;

[0033] (3) Add water to the interlayer between the gold bushing tube and the autoclave, seal the autoclave, and then place the sealed autoclave in a resistance furnace for constant temperature and pressure treatment at 600℃ and 125MPa for 5 days; the filling degree of the water added to the interlayer between the gold bushing tube and the autoclave is 45%.

[0034] (4) The resistance furnace was set to a cooling rate of 10℃ / h. After the furnace temperature dropped to 100℃, it was rapidly cooled to room temperature to obtain millimeter-sized cubic KTN single crystals. The KTN single crystal was measured using vernier calipers, and the crystal size was 5.76mm × 5.67mm × 2.32mm. Figure 3 )

[0035] Example 2

[0036] (1) Take 10g of KTN crystals with poor uniformity prepared by the Czochralski method and place them at the bottom of the gold bushing tube, then add a mineralizing agent solution; the mineralizing agent is 10mol / L KNO3; the total filling degree of KTN raw material and mineralizing agent solution is 55% of the gold bushing tube.

[0037] (2) After sealing the gold bushing, place it in the body of the autoclave;

[0038] (3) Add water to the interlayer between the gold bushing tube and the autoclave, seal the autoclave, and then place the sealed autoclave in a resistance furnace for constant temperature and pressure treatment at 600℃ and 125MPa for 10 days; the filling degree of the water added to the interlayer between the gold bushing tube and the autoclave is 45%.

[0039] (4) Set the resistance furnace to a cooling rate of 8℃ / h. After the resistance furnace temperature drops to 100℃, quickly cool it down to room temperature to obtain a 1-2mm millimeter-scale cubic phase KTN single crystal.

[0040] Example 3

[0041] (1) Take 10g of the remaining KTN scrap prepared by the Claymore method and place it at the bottom of the gold bushing, then add the mineralizing agent solution; the mineralizing agent is 6mol / L KF; the total filling degree of KTN raw material and mineralizing agent solution is 45% of the gold bushing.

[0042] (2) After sealing the gold bushing, place it in the body of the autoclave;

[0043] (3) Add water to the interlayer between the gold bushing tube and the autoclave, seal the autoclave, and then place the sealed autoclave in a resistance furnace for constant temperature and pressure treatment at 550℃ and 100MPa for 8 days; the filling degree of the water added to the interlayer between the gold bushing tube and the autoclave is 45%.

[0044] (4) Set the resistance furnace to a cooling rate of 10℃ / h. After the resistance furnace temperature drops to 100℃, quickly cool it down to room temperature to obtain a 1mm-sized cubic phase KTN single crystal.

[0045] Example 4

[0046] (1) Take 10g of KTN crystals with poor uniformity prepared by the Czochralski method and place them at the bottom of the gold bushing tube, and then add a mineralizing agent solution; the mineralizing agent is a mixture of 10mol / L KOH and 6mol / L KF solution in a 1:1 mass ratio; the total filling degree of KTN raw material and mineralizing agent solution is 60% of the gold bushing tube.

[0047] (2) After sealing the gold bushing, place it in the body of the autoclave;

[0048] (3) Add water to the interlayer between the gold bushing tube and the autoclave, seal the autoclave, and then place the sealed autoclave in a resistance furnace for constant temperature and pressure treatment at 550℃ and 100MPa for 5 days; the filling degree of the water added to the interlayer between the gold bushing tube and the autoclave is 45%.

[0049] (4) Set the resistance furnace to a cooling rate of 6℃ / h. After the resistance furnace temperature drops to 100℃, quickly cool it down to room temperature to obtain a 1mm-sized cubic phase KTN single crystal.

[0050] Example 5

[0051] (1) Take 10g of the remaining KTN scrap prepared by the pulling method and place it at the bottom of the gold bushing tube, then add the mineralizing agent solution; the mineralizing agent is a mixture of 20mol / L KOH and 10mol / L KNO3 solution in a mass ratio of 2:1; the total filling degree of KTN raw material and mineralizing agent solution is 60% of the gold bushing tube.

[0052] (2) After sealing the gold bushing, place it in the body of the autoclave;

[0053] (3) Add water to the interlayer between the gold bushing tube and the autoclave, seal the autoclave, and then place the sealed autoclave in a resistance furnace for constant temperature and pressure treatment at 500℃ and 80MPa for 5 days; the filling degree of the water added to the interlayer between the gold bushing tube and the autoclave is 45%.

[0054] (4) Set the resistance furnace to a cooling rate of 5℃ / h. After the resistance furnace temperature drops to 100℃, quickly cool it down to room temperature to obtain a 1mm-sized cubic phase KTN single crystal.

[0055] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a millimeter-sized pure cubic phase KTN single crystal, characterized by, The method comprises the following steps: (1) placing KTN raw material at the bottom of a gold bushing tube, and then adding a mineralizer solution; the mineralizer solution is a mixed solution of one or more of KOH, KNO3 and KF; the concentration of the mineralizer solution is 6-20 mol / L; the total filling degree of the KTN raw material and the mineralizer solution is 45-60% of the gold bushing tube; (2) sealing the gold bushing tube and placing it in the kettle body of an autoclave; (3) adding water in the interlayer of the gold bushing tube and the kettle body, sealing the autoclave, and then placing the sealed autoclave in an electric resistance furnace for constant-temperature and constant-pressure treatment; the filling degree of the water added in the interlayer of the gold bushing tube and the kettle body is 45%; the temperature of the electric resistance furnace is 500-600 DEG C, the pressure is 80-150 MPa, and the constant-temperature treatment time is 5-10 days; (4) setting the cooling rate of the electric resistance furnace to 1-10 DEG C / h, and then rapidly cooling to room temperature after the temperature of the electric resistance furnace is reduced to 100 DEG C, to obtain a millimeter-level cubic-phase KTN single crystal.

2. The method of claim 1, wherein the method is characterized by: In step (1), the KTN raw material is ground solid-phase sintered KTN polycrystal or KTN crystal with poor uniformity prepared by a pulling method or KTN leftover material.

3. The method of claim 2, wherein the method is characterized by: The ground solid-phase sintered KTN polycrystal is undersize material sieved by a 100-mesh sieve.

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